Gas analyzer system with ion source
A gas analyzer system uses an ionization source, which can be a hot cathode ionization source. A magnet assembly is positioned to define a magnetic field, which permits separation of ion components based on their mass to charge ratio. An ion beam deflector is used, such as a pair of deflector plates, which can scan ion components across a detector. The ion beam deflector defines a deflection electric field across the magnetic field and across a direction of travel of the ions emitted from the ionization source.
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There is an ongoing need to facilitate trouble shooting in high vacuum processes. High vacuum processes typically follow a workflow that starts with a pump down of a vacuum chamber from atmospheric pressure. The user tracks the pressure of the vacuum chamber during the pump down and, when the total pressure meets a target pressure, the vacuum process or experiment can start. There is generally an expectation that the target pressure will be met within a pre-specified time range. If the target pressure is not reached after an expected period of time, or it takes longer than usual to reach it, the vacuum system user needs to troubleshoot the vacuum chamber. Often, troubleshooting requires not only using an ionization gauge, but also the need to break vacuum to use a helium leak detector, and sometimes, to use an expensive Residual Gas Analyzer to measure water levels.
There is, therefore, an ongoing need to provide equipment that reduces the time and expense involved in troubleshooting high vacuum processes. In addition, there is a need for improved systems for helium leak detection, water percentage determination, magnetic sectors, quadrupole mass filters and other systems that use an ionization source.
SUMMARYA gas analyzer system uses an ionization source, which can be a hot cathode ionization source; a magnet assembly positioned to define a magnetic field, which permits separation of ion components based on their mass to charge ratio; and an ion beam deflector, such as a pair of deflector plates that can scan ion components across a detector. The ion beam deflector defines a deflection electric field across the magnetic field and across a direction of travel of the ions emitted from the ionization source. The arrangement can provide ions with a narrow energy distribution that can produce a mass spectrum with sharp peaks, having high resolution. Other advantages are described further below.
A gas analyzer system comprises an ionization source configured to create a source electric field in an ionization region of the ionization source. The ionization region receives a gas from a monitored chamber such that ions of the gas are formed in the ionization source. A source aperture is positioned to emit a portion of the ions of the gas out of the ionization source, the ions being accelerated by the source electric field in a direction towards the source aperture. A magnet assembly is positioned to define a magnetic field to angularly displace the emitted portion of the ions based on a mass to charge ratio of ions of the gas. An ion beam deflector is positioned between the source aperture and the detector, the ion beam deflector defining a deflection electric field across the magnetic field and across a direction of travel of the emitted portion of the ions. A detector is positioned to detect a displaced ion component of the emitted portion of the ions. Ion current measurement circuitry is electrically connected to measure a current produced from receipt of the displaced ion component at the detector.
The ionization source may comprise a cold cathode ionization source or a hot cathode ionization source. The hot cathode ionization source may comprise a hot filament and an electron collector configured to create an electron beam through the ionization source between the hot filament and the electron collector. The hot filament and the electron collector may be configured to create the electron beam in a direction parallel to the source aperture, the source aperture comprising an aperture elongated in the direction parallel to the electron beam. The system may further comprise an energy filter. The source aperture may comprise an elongated aperture, and the energy filter may comprise an energy filter grid positioned in an ion beam path of the emitted portion of the ions, the energy filter grid comprising conductive filaments oriented substantially perpendicular to the elongated aperture of the source aperture, and comprising substantially no conductive filaments oriented substantially parallel to the elongated aperture of the source aperture. The energy filter may comprise an entry grid positioned between the source aperture and an entry of an ion beam of the emitted portion of the ions into the ion beam deflector; and may comprise an exit grid positioned between an exit of an ion beam of the emitted portion of the ions out of the ion beam deflector, and the detector aperture.
The ion beam deflector may be configured to align an ion beam of the emitted portion of the ions on the detector. The ion beam deflector may comprise a pair of parallel plates, and may comprise a pair of curved plates. The source aperture may be positioned to emit a portion of the ions of the gas out of the ionization source to enter the ion beam deflector closer to one side of the ion beam deflector than a geometrical center of the ion beam deflector. A deflector power supply may be electrically connected to the ion beam deflector to create the deflection electric field between a pair of deflector plates of the ion beam deflector. The deflector power supply may be electrically connected to (i) provide a positive deflector bias voltage to a first deflector plate of the ion beam deflector relative to a ground voltage of a second deflector plate of the ion beam deflector, or (ii) provide a negative deflector bias voltage to the first deflector plate relative to the ground voltage of the second deflector plate, or (iii) provide a first deflector bias voltage to the first deflector plate and a second deflector bias voltage to the second deflector plate.
A deflector control circuit may be configured to supply a deflector control signal to the deflector power supply. The deflector control circuit may be configured to control a voltage of the deflector power supply to cause the ion beam deflector to direct displaced ion components having different energies and a common ion component mass to be focused through a detector aperture of the detector. The deflector control circuit may be configured to vary a voltage of the deflector power supply to cause the ion beam deflector to vary a deflection of the displaced ion component of the emitted portion of the ions. The voltage of the deflector power supply may be varied based on (i) a triangular sawtooth variation of the voltage with time, or (ii) a voltage waveform to control a peak width and temporal position, relative to other ion components, of the displaced ion component. The deflector control circuit may be configured to scan a voltage of the deflector power supply to cause the ion beam deflector to deflect plural ion components to be detected by the detector in succession as the voltage of the deflector power supply is scanned; and may be configured to scan the voltage of the deflector power supply to permit detection of a mass spectrum of the plural ion components. Total current measurement circuitry can be electrically connected to measure a total ion current of the ionization source.
The foregoing will be apparent from the following more particular description of example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments.
A description of example embodiments follows.
In a prior application naming some of the inventors of the present application, there was disclosed a cold cathode ionization source for a gas analyzer system; see U.S. patent application Ser. No. 16/397,436 of Brucker et al., filed Apr. 29, 2019, entitled “Gas Analysis with an Inverted Magnetron Source,” the entire teachings of which are incorporated herein by reference. The disclosure of that application taught the use of a cold cathode ionization source in which a magnetic field is oriented across an electric field, and the use of an ion beam deflector to permit sweeping of an ion beam and ion components across a detector aperture, thereby permitting generating a spectrum of ion components.
Although the cold cathode ionization sources taught in that application provide many benefits, the teachings of that application can be extended to a hot cathode ionization source. Also, additional features can be applied to both hot cathode and cold cathode ionization sources. Taught herein is a gas analyzer system that uses an ionization source, which can be a hot cathode ionization source. A magnet assembly is positioned to define a magnetic field, which permits separation of ion components based on their mass to charge ratio. An ion beam deflector is used, such as a pair of deflector plates, which can scan ion components across a detector. The ion beam deflector defines a deflection electric field across the magnetic field and across a direction of travel of the ions emitted from the ionization source. Among other potential advantages, ions are generated with a narrower energy distribution, which produces sharper peaks in the mass spectrum, thereby providing high resolution. Other potential advantages are taught herein.
The gas analyzer system will first be described with reference to
In
A vacuum port 148 permits gas from the monitored chamber to enter the gas analyzer system from the monitored chamber, so that the gas travels in a counter-flow direction to the ion beam, that is, the gas travels in the direction from the detector 116 towards the source aperture 114. At the ionization source 104, the gas enters the ionization source 104 (for example, through an opening in the top of the ionization source 104 or in some versions through open or perforated sides of the ionization source 104), and then is ionized inside the ionization source 104 to form the ion beam, which is emitted in the reverse direction, that is, the ion beam travels from the source aperture 114 towards the detector 116.
A detector 116 (see
An ion beam deflector 118 is positioned between the source aperture 114 and the detector 116. The ion beam deflector 118 defines a deflection electric field across the magnetic field (see direction 860 in
In addition, the system of
As shown in
In the embodiment of
In
In addition, in the embodiment of
Scanning a voltage on one or both of the deflector plates, such as by scanning a voltage on a pusher deflector plate 646a, and plotting the ion component signal (such as a partial pressure current) versus the voltage on the deflector plate, allows the generation of a real-time mass spectrum. For example, a graphic display can be created on a visual display device, showing detected partial pressure current in volts, provided by a pico-ammeter current to voltage converter, on the vertical axis, and time in seconds, which is linearly related to the voltage on the deflector plate (because the deflector voltage is swept with a sawtooth waveform), on the horizontal axis. In addition, automatic zero baseline subtraction can be performed.
In
In
In another version of the embodiment of
In addition, the ion beam deflector 118 can be used to determine spectral baseline offsets, by measuring at the top and the side of spectral peaks. This can also provide an advantage over conventional helium leak detectors.
In another embodiment, the ionization source can comprise a cold cathode ionization source.
As with the hot cathode ionization source embodiment, displaced ion components 968 are separated into different ion components, which diverge increasingly from each other as they travel further from the source aperture 114. In the inverted magnetron cold cathode discharge electrode configuration, the cathode electrode assembly 1184 surrounds the anode electrode 1186. An axial magnetic field (created using a magnet assembly 264, not shown in
In addition, in the embodiment of
As used herein, a hot cathode ionization source can include any hot cathode ionization source, including those based on incandescent filaments and those using thermionic emission. In addition, other ionization sources can be used, including cold cathode ionization emitters, such as Electron Generator Arrays and Field Emitters. Hot cathode ionization sources are generally more complex than cold cathode ionization sources. However, hot cathode ionization sources provide ions with smaller energy distributions, which can lead to improved resolving power.
Systems taught herein can be used in a variety of different possible contexts, including, for example, as helium sensors in helium leak detectors; in mass spectrometers; in magnetic sectors; and for multi-gas detection.
A variety of different possible advantages can be achieved using embodiments taught herein. Ions can be generated with a narrower energy distribution, which translates into sharper peaks in the mass spectrum. This provides high resolution. In addition, the energy of the ions can be independent of pressure. The ion signal is linearly related to pressure, making quantification easier, since no complicated non-linear look-up tables are required. There is no change in ion energy with pressure, meaning that the peak locations and filter voltage do not need to be adjusted versus pressure, or the adjustments are smaller. A smaller size helium sensor can be provided for a helium leak detector, which provides an opportunity to reduce the size of current mass spectrometers. Compared to standard helium sensors in helium leak detectors, the ability to scan eliminates the need to use 180-degree bends, making the detectors much more compact. In addition, there is no need to adjust filament location, as is commonly done during the tuning of helium leak detectors. Instead, with the help of deflection plates, any changes in the location of the ion beams can be compensated with adjustments to the deflection plate voltage.
Further, the high energy source taught herein can be very efficient, in that the components of the system work well together. The same anode potential that energizes the ions, also attracts the electrons to the ionization region. The fact that the flight path is at ground reduces the chances for arcing or electrical shock. The voltages required are fairly small and easy to implement in electronics. With low potentials to start with, there can be ensured a small range energy distribution for the ions, resulting in well resolved spectra.
The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims.
Claims
1. A gas analyzer system, the system comprising:
- an ionization source configured to create a source electric field in an ionization region of the ionization source, the ionization region receiving a gas from a monitored chamber such that ions of the gas are formed in the ionization source;
- a source aperture positioned to emit a portion of the ions of the gas out of the ionization source, the ions being accelerated by the source electric field in a direction towards the source aperture;
- a magnet assembly positioned to define a magnetic field to angularly displace the emitted portion of the ions based on a mass to charge ratio of ions of the gas;
- an ion beam deflector positioned between the source aperture and the detector, the ion beam deflector defining a deflection electric field across the magnetic field and across a direction of travel of the emitted portion of the ions;
- a detector positioned to detect a displaced ion component of the emitted portion of the ions; and
- ion current measurement circuitry electrically connected to measure a current produced from receipt of the displaced ion component at the detector.
2. The gas analyzer system of claim 1, wherein the ionization source comprises a cold cathode ionization source.
3. The gas analyzer system of claim 1, wherein the ionization source comprises a hot cathode ionization source.
4. The gas analyzer system of claim 3, wherein the hot cathode ionization source comprises a hot filament and an electron collector configured to create an electron beam through the ionization source between the hot filament and the electron collector.
5. The gas analyzer system of claim 4, wherein the hot filament and the electron collector are configured to create the electron beam in a direction parallel to the source aperture, the source aperture comprising an aperture elongated in the direction parallel to the electron beam.
6. The gas analyzer system of claim 1, further comprising an energy filter.
7. The gas analyzer system of claim 6, wherein the source aperture comprises an elongated aperture, and wherein the energy filter comprises an energy filter grid positioned in an ion beam path of the emitted portion of the ions, the energy filter grid comprising conductive filaments oriented substantially perpendicular to the elongated aperture of the source aperture, and comprising substantially no conductive filaments oriented substantially parallel to the elongated aperture of the source aperture.
8. The gas analyzer system of claim 6, wherein the energy filter comprises an entry grid positioned between the source aperture and an entry of an ion beam of the emitted portion of the ions into the ion beam deflector.
9. The gas analyzer system of claim 6, wherein the energy filter comprises an exit grid positioned between an exit of an ion beam of the emitted portion of the ions out of the ion beam deflector, and the detector aperture.
10. The gas analyzer system of claim 1, wherein the ion beam deflector is configured to align an ion beam of the emitted portion of the ions on the detector.
11. The gas analyzer system of claim 1, wherein the ion beam deflector comprises a pair of parallel plates.
12. The gas analyzer system of claim 1, wherein the ion beam deflector comprises a pair of curved plates.
13. The gas analyzer system of claim 1, wherein the source aperture is positioned to emit a portion of the ions of the gas out of the ionization source to enter the ion beam deflector closer to one side of the ion beam deflector than a geometrical center of the ion beam deflector.
14. The gas analyzer system of claim 1, further comprising a deflector power supply electrically connected to the ion beam deflector to create the deflection electric field between a pair of deflector plates of the ion beam deflector.
15. The gas analyzer system of claim 14, wherein the deflector power supply is electrically connected to (i) provide a positive deflector bias voltage to a first deflector plate of the ion beam deflector relative to a ground voltage of a second deflector plate of the ion beam deflector, or (ii) provide a negative deflector bias voltage to the first deflector plate relative to the ground voltage of the second deflector plate, or (iii) provide a first deflector bias voltage to the first deflector plate and a second deflector bias voltage to the second deflector plate.
16. The gas analyzer system of claim 14 or 15, further comprising a deflector control circuit configured to supply a deflector control signal to the deflector power supply.
17. The gas analyzer system of claim 16, wherein the deflector control circuit is configured to control a voltage of the deflector power supply to cause the ion beam deflector to direct displaced ion components having different energies and a common ion component mass to be focused through a detector aperture of the detector.
18. The gas analyzer system of claim 16, wherein the deflector control circuit is configured to vary a voltage of the deflector power supply to cause the ion beam deflector to vary a deflection of the displaced ion component of the emitted portion of the ions.
19. The gas analyzer system of claim 18, wherein the deflector control circuit is configured to vary the voltage of the deflector power supply based on (i) a triangular sawtooth variation of the voltage with time, or (ii) a voltage waveform to control a peak width and temporal position, relative to other ion components, of the displaced ion component.
20. The gas analyzer system of claim 16, wherein the deflector control circuit is configured to scan a voltage of the deflector power supply to cause the ion beam deflector to deflect plural ion components to be detected by the detector in succession as the voltage of the deflector power supply is scanned.
21. The gas analyzer system of claim 20, wherein the deflector control circuit is configured to scan the voltage of the deflector power supply to permit detection of a mass spectrum of the plural ion components.
22. The gas analyzer of claim 1, further comprising total current measurement circuitry electrically connected to measure a total ion current of the ionization source.
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Type: Grant
Filed: Nov 27, 2019
Date of Patent: Mar 16, 2021
Assignee: MKS Instruments, Inc. (Andover, MA)
Inventors: Gerardo A. Brucker (Longmont, CO), Timothy C. Swinney (Fort Collins, CO), Clinton L. Percy (Windsor, CO)
Primary Examiner: Michael Maskell
Application Number: 16/698,178
International Classification: H01J 49/00 (20060101); G01N 27/622 (20210101); H01J 37/317 (20060101);